I record a lot of in-depth 1-on-1 video interviews in a small studio with good sound treatment and acoustics.

I'm using Rode Lavalier's but more commonly that not I'm having an audio spill issue, I'm not sure if this is the correct term!

But basically, I get the level matching for the presenter and guest so I have them at the same volume, but I find when each speaks they frequently get picked up by the other's mic.

They are sat around 2 feet apart, ideally I'd have them further apart but I don't really have the room to accomodate this.

So I find myself having to constantly bring down the fader slightly of the person who isn't talking at the time so it doesn't pick up the other person talking then quickly bring it back up when the other starts talking.

I originally used cardioid mic's that came with the Sennheiser Presentation Wireless systems (the really cheap ones) - we recently upgraded to the Sennheiser G3 system which did come with the omni-directional version of their lav mics, but at the time - I thought it would be a good idea to upgrade the mics and thought the Rode Lavaliers would be a good choice as I had read good reviews on them.

I had hoped the change from cardionid to omni-directional would help, which it has in that they can now be worn upside down and when the presenter or guest turns there head, they can still be heard, but still in most interview's we do, I'm having this audio spill problem.

The presenter does have a tendency to talk slightly louder than the guest, but surley this is common that one person is louder, or is this my problem?

If anyone has any tips, ideas or suggestions - I would be most grateful... I'd just love to be able to gets the mic's setup and be confident to not have to make too many adjustments as my hands are needed on many other buttons during a recording!

As long as they don't over-talk each other, spill shouldn't be an unfix-able problem. Record each mic on a separate track and take care of the mix-down in post. (You'll be busier than a one-armed wallpaper hanger trying to juggle the faders mixing as you shoot.) In post pan both tracks equally to the centre and while one person is speaking, mute the other track. Cover silences with room tone.

Good idea to use omnis ... won't help the spill but will give more consistent results as the talent moves their head because they won't be going on- and off- mic. Cardioid lavs are pretty much designed for controlling feedback in sound reinforcement PA applications and are not used much for film/video recording.

It isn't completely clear whether you are mixing live (as for a live show) or recording the interviews for post-production?
If you are doing this live, you could use an automatic mixer to "duck" the mic that isn't in use.

Or in post-production, you could use a similar software function to automate the process. Of course, you would be recording each mic to a separate channel.

It is not uncommon for one person (typically the interviewer) to talk louder. That is expected and must be accommodated. Omni mics make head-turning problem better, but they actually make the cross-talk problem worse.

Given the constraints of your space, there is no other mic technique that would improve the situation except getting the mics closer to the mouths. That would take something like the (Rode or others') headset mic. That would increase the ratio (difference) between the desired sound and the ambient noise (including the other talker's speech).

You have "small room syndrome." Been there. Don't like it. Have you treated the ceiling? The floor?

An automixer can help. I have used a Shure FP410 to some good effect.

The use of cardioid mics can help, but cardioid mics are problematic. Omnis mounted up high close to the tie knot helps. You can also improve the sound by using mics like the Countryman E6. Being on the cheek, and closer to the mouth, you get a much tighter sound. You may have to wrestle the DP or director to the mat, but if you put the mics on the off-camera cheek, you minimize their appearance and everything will sound a LOT better.

Last time I was in this position, I ran mics through an automixer to one track for a mix, and isoed each mic to a separate track in case I didn't like my mix.

Our studios once got a contract for miles of this pre-recorded stuff and we had all sorts of trouble with multiple lav spill on non pro speakers
with all voice levels, lisps, nasal, clicks, buck teeth, raspy breathers and other speech impediments. (I thought it would never stop)

The way we handled it was to use audio gates in our NLEs on each of the lavs. You have to use a very fast attack time to stop clipping the speakers first syllable as his gate opened, so we copied every voice track to an adjacent track and advanced it a few millisecs, to trigger the relavent gate to open.

Setting the threshold for each gate was another hurdle which our guys overcame with experience.

I've also used the Shure 410 and 810 auto mixers, which generally work good, however.. they ain't fool-proof... so I would not recommend them to the inexperienced. Same with noise gates, unless it's non-destructive (can be undone) in post. I generally find noise gates and not suitable for dialog, (you can hear them opening/closing, when I do us them, it's in an expander configuration.. which isn't always an option which cheap/free plug-ins.

I think your idea of running both mics into a mixer, and then running the mixer output through a compresser/limiter, is contrary to the best suggestions that have been made.

You will get the best results if you record each mic on a separate track, then switch between tracks (depending on which person is speaking) when you do the final mix.

You simply need to set your levels conservatively before you start recording. Have each person speak "fairly loud" and set level so there's plenty of headroom. And then monitor levels while recording to be sure you don't need to reduce the gain further. That should give you two clean tracks, one for each person. Then just mix as recommended: do a quick crossfade at the point where a different person starts to talk. Mostly you will have one track up and one down (except for the few seconds when one person talks over the other one). That eliminates problems of one given voice being on both mics/tracks.

But I really need to get the compressor / limiter acting in a useful way! And stopping the audio peaking.

The use of compressors is a bit of an artistic thing people use them in many ways, but give this a go as a starting point...

Connect the compressors into the master o/p area of the desk via inserts or output or even groups.
put tone into the chain with the comp. in bypass set the tone on the desk to -3 on the VU meter, switch comp in, adjust the ratio to about 3:1 and adjust the threshold until the first LED is just lit up.
Switch the comp out of the chain, push the tone level up a bit, set 0vu on the meter, switch the comp in, then adjust the comp o/p knob to match 0vu, this will give a very slight soft holding on your mix without being to savage probably ideal for chat / interviews.

Music might be a bit heavier with lower threshold or greater ratio. In a V/O booth you might want to run it at -5 threshold with a 6:1 ratio to give the voice a bit of punch.....
Set the attack and release on fast settings as a starting point and take it from there.

As opposed to what Brian suggests, I often use the stereo limiter in my Sound Devices 442 mixer as peak stops before the next stage. They do a very nice job and the trip through the 442 is a high quality trip. I think they used the same topology in the 552.